1. Field of the Invention
Embodiments described herein pertain to the field of diagnosing and treating the spine, particularly lower back pain. Embodiments relate to methods for diagnosing and/or treating disorders causative, or being precursors to back pain. In particular embodiments relate to methods of increasing angiogenesis in specifically diagnosed conditions associated with back pain.
2. Related Art
Musculoskeletal disorders of the spine are an extremely common occurrence associated with debilitating back pain, leading to enormous psychosocial and economic ramifications. Lower-back pain is the leading source of disability in people under 45 years of age, and it results in significant economic losses (Frymoyer J W, et al. The Adult Spine: Principles and Practice, 143-150, 1997). Eighty percent of people in the United States will experience back pain at some point in their lifetime (Lively, M. W., South Med J, 95:642-646, 2002), and it is the second most common reason for symptomatic physician visits (Hart, L. G. et al. Spine 20:11-19, 1995). Causes of back pain range from injury, which presents as a minor problem, accelerating to a chronic disorder, as well as degenerative spine diseases that lead to degenerative spondylolisthesis and spinal stenosis. The vast majority of chronic back pain is associated with degeneration of the intervertebral disc, which can manifest in many different clinical conditions including spinal stenosis and instability, radiculopathy, myelopathy, and disc herniation. In order to attain proper understanding of spinal pain, particularly lower back pain, we will review some of the anatomy of the spine, particularly the lumbar area.
The human spine is composed of bony structures called vertebrae, separated by intervertebral discs. One of the main functions of the vertebrae is to provide structural support and protection for the spinal cord. Each vertebra includes a spinous process, a bony prominence behind the spinal cord, which shields the cord's nervous tissue on the back side, two bony protrusions on the sides called transverse processes, and a “body” in front of the spinal cord which provides a structural support for weight bearing. The average adult has 24 vertebrae, although at birth 33 are present. Reduction in the number of vertebrae is caused by fusion during normal development. The vertebrae are divided by anatomical locations with 7 in the neck, also called the cervical vertebrae, 12 in the middle back, called the thoracic vertebrae, 5 in the lower back, called the lumbar vertebrae, and the sacrum, which is actually formed from five fused vertebrae. The tailbone, called the coccyx is made of three fused vertebrae. Of these, the lumbar vertebrae are the largest, in part since they are responsible for carrying the majority of body weight. Consequently, the lumbar area is associated with the highest level of degeneration and is believed causative for a wide variety of pain-inducing syndromes.
Separating the vertebrae are soft intervertebral discs that, together with the two facet joints, allow for movement of the vertebrae and therefore provide the ability of the spine to move in various directions. The complex of two facet joints posteriorly and the disc anteriorly is referred to as a spinal segment. The intervertebral disc includes the annulus fibrosus, the nucleus pulposus, and the cartilage endplate. The nucleus pulposus includes anionic proteoglycans, such as aggrecan, that have high affinity for water, and provide a cushioning and shock-absorbing function. The annulus fibrosus encapsulates the nucleus pulposus, and is composed of concentrically organized layers of collagen fibrils (lamellae). The composition of the nucleus pulposus is distinctly different than the annulus fibrosus since the former primarily includes a jelly-like substance and high collagen type I, whereas the latter is made of a solid, fibrotic-like texture, primarily containing collagen type II. In an adult, the cartilage endplate is composed primarily of hyaline cartilage and serves to separate the nucleus pulposus and annulus fibrosus from the adjacent vertebral bone. Discogenic pain often arises from areas of the annulus fibrosus. As a matter of fact, pain-associated molecules such as Substance P and TNF (Tumor Necrosis Factor) have been identified in large concentrations in biopsy samples of patients suffering discogenic pain, but not in controls.
Each disc provides motion and binds the segments together through its 95% non-cellular and 5% cellular components. Nutrition to the disc cells (or chondrocytes) is provided by arteries that branch off of the major artery in the body (called the aorta) and wrap around each vertebral body, penetrating the bone along its circumference. The arteries course through the vertebral body (bone) and then turn towards the disc at either end. The oxygen, glucose and other nutrients are “dropped off” where the disc attaches to the bone and the capillaries and venules form a vascular loop. The cartilage that is in contact with these vascular loops is called the “endplate.” The nutrients “diffuse” (or move through the endplate and disc tissue without being transported in blood vessels) into the middle of the disc (or nucleus). In addition to this pathway, arterioles deliver nutrients to the outer edge of the disc (annulus) directly (this pathway provides minimal nutrients to the nucleus in normal discs but might be exploited in angiogenic treatment). Once the nutrients reach the cell, they are taken up and utilized for the manufacture of the materials that make up the disc (extracellular matrix: collagen and proteoglycans). Recent studies have demonstrated that cartilage cells require oxygen to produce enough energy for the proper manufacture and maintenance of the extracellular matrix. If the cells do not receive enough oxygen, the manufacturing process diminishes and the disc becomes acidic (pH drops) (Homer, H et al. Spine 26:2543-2549, 2001). As the nutrient supply is cut off, the cells in the disc begin to die and the disc tissue begins to breakdown. This loss of nutrients is thought to be the initial cause of degenerative disc disease. As the disc continues to degenerate and the cell population decreases, the oxygen concentration may return to normal due to less demand. At this stage, regeneration still may be a possibility. However, excessive mechanical loading on a weakened structure precipitates further degeneration which may lead to structural defects such as endplate fracture, radial fissures and herniation. As cells continue to produce energy through anaerobic processes, low pH creates further cell death.
This nutrient supply can be blocked at various stages. The feeding arteries themselves can narrow due to atherosclerosis with resultant ischemia of the vertebral body. With less blood flowing through the vertebrae, less oxygen and nutrients are available to diffuse into the disc creating hypoxia, lower pH and cell death (Kauppila, L et al. Spine 22:1642-1649, 1997; Kurunlahit, M et al. Radiology 221:779-786, 2001). In addition to narrowing of the major lumbar vessels, many studies have demonstrated decreasing blood flow within the vertebral body as the reason for the loss of nutrients and degenerative disc disease. Degenerative disc disease due to nicotine and aging demonstrate a loss of nutritive blood vessels in the area supplying nutrients (Iwahahi, M et al. Spine 27:1396-1401, 2002; Boos, N et al. Spine: 27:2631-2644, 2002). Eventually, the endplate itself can become a hindrance to the diffusion of nutrients creating another obstacle to proper disc chondrocyte nutrition (Rajasekaran, S et al. Spine 29:2654-2667, 2004).
Although disc degeneration continues to have a tremendous and ever-increasing impact worldwide, current treatment options do not address the underlying cause. Current treatments include bed rest, nonsteroidal anti-inflammatory medication in the early phases of pathology, and procedures such as discectomy, arthroplasty, (joint replacement), injection of artificial nucleus pulposus and fusion in the later phases when the prior approaches did not ameliorate pain. Such approaches are unpredictable, and deal almost exclusively with end-stage clinical manifestations, and therefore do nothing to alter the disease process itself. Additionally, procedures such as vertebral fusion result in the increased incidence of disc degeneration in the adjacent discs due to alterations in the biomechanical distribution of work-load.
Recent advances in both biotechnology and our understanding of the biochemical makeup and environment of the intervertebral disc have led to increased interest in the process of degeneration and the possibility of developing novel treatments aimed directly at disc preservation. Certain genes found to have significant impact on matrix synthesis and catabolism within the disc have provided targets for scientists seeking to alter the balance between the two. To this end, much attention over the past several years has centered on gene therapy, and these efforts have yielded some promising preclinical results with regard to its use in treating disc degeneration (Levicoff, E. A. et al. Spine J 5:2878-2968, 2005). Unfortunately, none of these approaches are near clinical implementation at the time of this writing. Additionally, it is important to note that even in the circumstance that disc regeneration alone can be achieved through gene therapy or other interventional means, the underlying process that originally caused the degeneration must be addressed in order to prevent recurrence.
Currently, no biological treatment is widely available for disc degeneration. However, many different molecules of potential therapeutic benefit are being investigated. The focus of molecular therapy has been to prevent or reverse one or more aspects of these changes in the disc extracellular matrix. At least four different classes of molecules may be effective in disc repair. These include anticatabolics, mitogens, chondrogenic morphogens and intracellular regulators (Yoon, S. T. Spine J 5:2808-2868, 2005; Masuda, K. et al. Spine 29:2757-2769, 2004; Shimer, A. L. et al. Spine 29:2770-2778, 2004). Hallmarks of disc degeneration include loss of proteoglycans, water, and Type II collagen in the disc matrix. Other changes in the matrix are less well defined, including loss of the higher molecular weight proteoglycans, collagen cross-linking and organization of the proteoglycan, etc. An important process in disc degeneration seems to be the change of the differentiated chondrocyte phenotype in the nucleus pulposus into a more fibrotic phenotype. Together these changes in the disc matrix lead to alterations of the disc and vertebral anatomy that ultimately are associated with a pathologic condition (Setton, L. A. et al. Spine 29:2710-2723, 2004; Roughley, P. J. Spine 29:2691-2699, 2004).
Due to the fact that matrix loss is a balance between matrix synthesis and degradation, it is possible to increase disc matrix by increasing synthesis or by decreasing degradation. One approach is to prevent matrix loss by inhibiting the degradative enzymes. Degenerated discs have elevated concentrations of matrix metalloproteinases (MMPs). Within the matrix, MMP activity is normally inhibited by tissue inhibitors of MMPs (TIMPs) (Roberts, S. et al. Spine 25:3005-3013, 2000; Nagase, H. et al. J Biol Chem 274:21491-21494, 1999; Wallach, C. J. et al. Spine 28:2331-2337, 2003). Wallach, et al. (Spine 28:2331-2337, 2003) tested whether one of these anticatabolic molecules, TIMP-1, could increase the accumulation of matrix proteoglycans with in vitro experiments. It was observed that TIMP-1 expression in disc cells increased accumulation and also increased the “measured synthesis rate” of proteoglycans (Wallach, et al. Spine 28:2331-2337, 2003). Chondrogenic morphogens are cytokines that not only possess mitogenic capability but are characterized by their ability to increase the chondrocyte-specific phenotype of the target cell. Most of the research in chondrogenic morphogens has been performed with transforming growth factor-β (TGF-β), bone morphogenetic proteins (BMPs) or growth and differentiation factors (GDFs). Chondrogenic morphogens are particularly attractive because they may reverse the fibrotic phenotype of disc cells to the more chondrocytic phenotype of disc nucleus cells in younger and more “normal” discs. By definition, these molecules are secreted molecules and hence can potentially act in autocrine, paracrine and endocrine fashion.
BMP-2 is another prototypic chondrogenic morphogen (Thompson, J. P. et al. Spine 16:253-260, 1991). Yoon, et al. (Spine 29:2603-2611, 2004) reported that recombinant human BMP-2 increased production of rat disc cell proteoglycans and significantly increased the chondrocytic phenotype of the disc cells as shown by increased aggrecan and Type II collagen gene expression, whereas there was no change in Type I collagen gene expression. Kim, et al. (J Neurosurg 99:291-297, 2003) reported that BMP-2 can partially reverse the inhibitory effect of nicotine on the synthesis of disc cell proteoglycan. BMP-7, also known as OP-1 (Osteogenic Protein-1), is another disc cell morphogen that has demonstrated potent in vitro activity in terms of enhancing matrix formation in disc cells (Masuda, K. et al. J Orthop Res 21:922-930, 2003; Zhang, Y. et al. Am J Phys Med Rehabil 85:515-521, 2004; Takegami, K. et al. Spine 27:1318-1325, 2002). Growth differentiation factor 5 (GDF-5) is also known as CDMP-1 (Cartilage-derived morphogenetic protein 1) and has also been considered for regeneration of disc cells. However, only in vitro experimentation has been performed to date (Chang, S. C. et al. J Biol Chem 269:28227-28234, 1994).
Intracellular regulators are a distinct class of molecules because they are not secreted and do not work through transmembrane receptors. These molecules are neither cytokines nor growth factors in the classical sense, and yet they can have effects that are quite similar to the secreted molecules discussed previously. This class of molecules typically controls one or more aspects of cellular differentiation. For instance, Sma-Mad (SMAD) proteins are intracellular molecules that mediate BMP-receptor signaling (Nohe, A. et al. Cell Signal 16:291-299, 2004; Hatakeyama, Y. et al. J Bone Joint Surg Am 85-A Suppl 3:13-18, 2003). Although there are no specific published papers on the effect of SMAD proteins on disc cells, proteins such as Smad-1 and Smad-5 are predicted to induce similar effects on disc cells as BMP-2, such as increasing proteoglycan and Type II collagen synthesis. Sox9 (transcription factor) is a chondrocyte marker that is a positive regulator of Type II collagen mRNA transcription (Yoon, S. T. Spine J 5:280 S-286S, 2005; Li, Y. et al. Tissue Eng 10:575-584, 2004; Aigner, T. et al. Matrix Biol 22:363-372, 2003). Paul, et al. (Spine 28:755-763, 2003) showed that Sox9 delivered by adenovirus can increase Sox9 expression and disc cell production of Type II collagen in in vitro experiments.
The success of a disc tissue engineering strategy is dependent on molecular cues to direct the differentiation of cells and affect their biosynthetic function. Many growth factors, including members of the transforming growth factor beta superfamily, affect the differentiation process of disc cells. This group of related proteins directs the induction of mesenchymal precursors to form mature skeletal tissues (Sampath, T. K. et al. Proc Natl Acad Sci USA 81:3419-3423, 1984). The activity of these molecules is complex and affects intercellular signaling pathways (Israel, D. I. et al. Growth Factors 13:291-300, 1996; Heldin, C. H. et al. Nature 390:465-471, 1997). In addition, concentration and timing of presentation of the growth factor influences its activity. Depending on the tissue, the effects of a given morphogen may be different. For instance, the osteogenic molecule bone morphogenetic protein-7-osteogenic protein-1 (BMP-7/0P-1) has been shown to have a dramatic effect on disc cells, increasing their metabolic output of matrix proteins and rescuing them from the detrimental effects of Interleukin 1 (IL-I) (Takegami, K. et al. Spine 27:1318-1325, 2002). This data suggests that growth factors could play a useful role in a cell-based tissue engineering strategy.
Other yet to be identified factors direct cell-to-cell communication and appear to play an important role in the viability and metabolic activity of disc cells. Yamamoto, et al. (Spine 29:1508-1514, 2004) showed that cell proliferation and proteoglycan synthesis was significantly enhanced in disc cells cultured in a system that allowed direct cell-cell contact with bone marrow-derived stromal cells. In another study, Hunter, et al. (Spine 29:1099-1104, 2004) reported that enzymatic disruption of gap junctions produced a negative effect on cell viability, suggesting that communication among adjacent cells plays a vital role in cellular viability and function, and therefore interventions supporting their enhancement may be beneficial.
The invention relates to methods for diagnosing, treating or ameliorating painful conditions of the spine, particularly lower back pain. Embodiments are directed to classification of back pain that is based on specific parameters associated with ischemia, which is a decrease blood flow inflow due to arterial blockage, hypoperfusion, which is diminished microvascular blood flow, and the resulting hypoxia, which is decreased oxygen within the tissue, with resultant damage to tissue. Further embodiments relate to treatments for alleviating the state of ischemia, hypopersion and hypoxia in patients that may lead to therapeutic improvement.